"Internally Balanced" = All balancing is done with in the (rotating Assy) crank rods and piston

"Externally Balanced"= Some balancing of the rotating Assy is done with counter weights in either or the Fly wheel or Balancer

If the engine is internal or external " balanced " has NOTHING to do with removing the only devise there is to help controle harmonics

Even if (and it isnt) the Zetec was externallly balanced and you removed it and replaced it with a solid (rubber removed) externally balancer you would still be removing the only way the engine has to controle harmonics

Were talking Harmonics here not the balance of the engine, Harmonics is VERY deadly to an engine and if Ford Enginers felt it was needed to go after groceries what do you think happens when you mod it and create higher RPM , Load... exactly you create more Harmonics

Its called a "harmonic balancer" to balance the engines harmonics NOT the engines rotating Assy